1. Field of the invention
The present invention relates to a sealing device providing more particularly for sealing upstream/downstream of a closure means.
It applies more particularly to closure means of the type including a closure member movable inside a tubular body and having, at its periphery, a sealing surface which, at the end of the closure stroke, is applied against a circular sealing liner, after a movement tangential or parallel to the main axis of symmetry of said sealing liner.
The invention also relates to closure means in which, in a reverse assembly, the bore of the body comprises a substantially conical sealing surface and the closure member is provided, at its periphery, with a liner providing static sealing with the closure member and dynamic sealing with said sealing surface.
In these types of closure means the sealing liner must therefore play a multiple role. It must at one and the same time provide static sealing, dynamic sealing and continuity of sealing between static sealing and dynamic sealing.
These sealing functions are particularly delicate to obtain particularly in the case when, because of the operating conditions of the closure means, the sealing liner must at one and the same time be made from a soft material capable of mating with the surface condition of the bearing surface of the seat so as to provide the best sealing, be made from a hard and rigid material capable of withstanding the mechanical forces due to the liner/seat contact pressure and the pressure of the fluid to seal, and yet be sufficiently flexible to make possible relative movements between the closure member and a body without adversely affecting the sealing.
In fact, in this case when, in the closed position of the closure means, the sealing surface of the closure member is not exactly centered on the dynamic sealing surface of the liner, this latter is not uniformly compressed, so that homogeneous sealing cannot be obtained all around the closure means. Thus, in the parts where the liner is highly compressed by the closure member, the closure means may withstand considerable pressures whereas, in the parts diametrically opposite these latter, the sealing is uncertain and the risks of leaks at high pressure are high.
2. Description of the Prior Art
To overcome these drawbacks, attempts have been made to equip the closure means with mechanisms for centering the closure member with respect to the sealing liner, these mechanisms concerning either the kinematics of the closure means or the closure means itself.
However, these solutions are complex, unreliable and result in a considerable increase of the cost price of the closure means.
It has also been proposed to produce the sealing liner in the form of a double flexible metal O-seal comprising:
a first flexible metal O-seal structure providing static sealing with the body of the closure means,
a second flexible metal O-seal structure providing the dynamic sealing,
a radial membrane made from a resilient material connecting the two sealing structures together while enveloping them at least partially so as to provide the continuity of sealing between static sealing an dynamic sealing, and at the same time allow self centering of the second seal structure on the sealing surface of the closure member, and
a floating reaction ring applied against the second seal structure opposite the zone of this structure where the sealing surface of the closure member bears.
Such a sealing liner which is described in the French patent n.degree. 77 22 976 of the Jul. 26, 1977 in the name of the applicant, entitled: "Double flexible O-seal", gives excellent results particularly in the case of valves or cocks intended to operate under conditions (high or low temperatures) for which the use of conventional elastomer liners is prohibited.
Despite these advantages, this liner nevertheless has a number of drawbacks.
First of all, it includes a removable reaction ring not secured to the assembly formed by the two O-seal structures and by the flexible membrane.
It is clear that this feature makes the fitting of the liner in the closure means more delicate with the risk of losing the reaction ring before assembly, for example during handling, storage, delivery or other operations, to which these liners are subjected.
Another drawback resulting from the structure of this liner consists in that it does not provide good initial centering of the reaction ring on the O-seal structure with which it cooperates for providing dynamic sealing of the closure means. Moreover, once the liner has been fitted in the closure means, the reaction ring enjoys a certain axial mobility which makes such centering hazardous. Furthermore, because of the disymmetric shape of the liner, the stresses exerted by the seal structure when it is subjected to the action of the closure means will tend to move this reaction ring axially while increasing decentering thereof.
Consequently, the reaction ring which will be loaded dissymmetrically will not be able to exert an optimum action on the seal structure and, particularly in the case where the closure stroke of the closure means is not parallel to the axis of the liner, the seal structure may in the long run become oval.
It may be finally noted that because of the disymmetry of the stresses which it receives the reaction ring must necessarily be formed from a solid part, to the exclusion of all other materials, possibly composite, which might be envisaged for increasing the flexibility of the sealing surface of the dynamic seal structure.